Pressure Assisted Aerial Retardant Delivery System

ABSTRACT

An aerial retardant delivery system comprising a retardant tank mountable in the fuselage of an aircraft. The tank includes a pressure opening in fluid communication with the fuselage such that pressure in the fuselage may act on retardant contained in the tank. The tank includes an outlet extending through a sidewall of the aircraft&#39;s fuselage, through which retardant may be delivered to a target. The system also includes a discharge gate operative to open and close the outlet. An actuation mechanism is disposed on the exterior of the tank and operatively coupled to the at least one discharge gate. A variable flow controller controls the discharge gate open position in order to provide retardant over a desired area of terrain. A one-way flapper is disposed in the pressure opening and is operative to allow pressure in the fuselage to enter the tank while inhibiting retardant from spilling from the tank.

CROSS REFERENCE TO RELATED APPLICATION

This application is continuation of US patent application entitled“Pressure Assisted Aerial Retardant Delivery System”, Ser. No.14/133,411, filed Dec. 18, 2013, which is a continuation of U.S. 371National Phase patent application entitled “Pressure Assisted VariableFlow Clean Throat Aerial Retardant Delivery System,” Ser. No.13/504,902, filed Aug. 20, 2012, which claims priority throughApplicants' prior U.S. PCT Patent Application entitled “PressureAssisted Variable Flow Clean Throat Aerial Retardant Delivery System,”Serial Number PCT/US11/58621, filed Oct. 31, 2011, which claims prioritythrough the Applicants' prior U.S. Provisional patent applicationentitled “Pressure Assisted Variable Flow Clean Throat Aerial RetardantDelivery System,” Ser. No. 61/408,459, filed Oct. 29, 2010, all of whichprior applications are hereby incorporated by reference in theirentirety. It is to be understood, however, that in the event of anyinconsistency between this specification and any informationincorporated by reference in this specification, this specificationshall govern.

BACKGROUND

Wildfires often erupt in remote areas having difficult terrain.Conditions such as high winds and dry weather may also cause a fire tobecome very large, very quickly resulting in an out of control fire thatthreatens woodland resources and developed areas alike. In order tocombat wildfires under such conditions firefighting aircraft, also knownas airtankers and water bombers, are often employed. The speed andcapacity of firefighting aircraft make them an important tool infighting larger, out of control fires. Particularly, where it is timeconsuming or unsafe to deploy firefighters and equipment on the ground.Firefighting aircraft can quickly deliver large quantities of fireretardant or water to an area to help control fires.

The density of retardant delivered to a given area of terrain is oftenreferred to as the coverage level rating. Coverage level ratings rangefrom 1 to 8, which are expressed in gallons of retardant per hundredsquare feet. For example, a coverage level rating of 4 corresponds to 4gallons of retardant per hundred square feet. Depending on the desiredcoverage level the required fire retardant flow rate discharged from afirefighting aircraft can reach 2000 gallons per second.

Conventional firefighting aircraft include a tank for carrying water orretardant and doors or gates that open to allow the payload to dischargeonto or in advance of the flames. Traditional retardant delivery systemsrely on gravity to propel the retardant through the gates. Accordingly,large gates are required to allow the retardant to flow from theaircraft at a sufficient rate to meet the higher coverage level ratings.With conventional firefighting aircraft the gates simply open anddischarge the retardant all at once. The pilot must therefore compensatefor the speed and altitude of the aircraft as well as the dischargecharacteristics of the delivery system in order to provide the desiredcoverage level in the desired area.

The payload of a typical firefighting aircraft is in the neighborhood of20,000 pounds of retardant or water. In order to support the weight ofthe retardant against the gates substantial opening/closing mechanismsare required. Also, traditional opening/closing mechanisms are locatedinside the tank in order to allow for support struts along the length ofthe gates. This configuration has the disadvantage of interfering withthe flow of retardant through the gates. Furthermore, typical retardantformulations include components that may be corrosive to the supportsand mechanisms that operate the gates, such that over time the supportsand or mechanisms may fail or at least require excessive maintenance.

Accordingly, there is a need for an aerial retardant delivery systemthat can assist the pilot in safely delivering a desired coverage levelto an area of terrain threatened by wildfire. There is a still furtherneed for a retardant delivery system gate opening/closing mechanism thatis configured for improved discharge characteristics as well as gatemechanism reliability and ease of maintenance.

SUMMARY

Provided herein is an aerial retardant delivery system that includes anaircraft having a pressurized cabin system. The aerial retardantdelivery system also includes a retardant tank located in the fuselageof the aircraft. The tank includes at least one opening that allows thecabin pressure to act on the retardant. In some embodiments the openingincludes a door or flapper panel that allows cabin pressure to enter thetank yet inhibits retardant from spilling from the tank. Accordingly,retardant may be discharged from the aircraft at a pressure differentialrelative to the exterior of the aircraft. In other words, the dischargeof retardant is pressure assisted. As a result, in some embodimentssmaller discharge gates may be used while maintaining discharge ratesrequired to meet coverage level ratings. The smaller discharge gatescan, in some instances, reduce the gate area exposed to the pressure ofthe retardant payload. Thus, the opening/closing mechanism is, incertain systems, less bulky than traditional mechanisms. Furthermore,the opening/closing mechanism is, in some applications, disposed on theexterior of the tank, thereby allowing unimpeded flow of retardantthrough the discharge gates which provides a clean throat dischargedesign. Locating the opening/closing mechanism outside of the tank alsohelps, in some embodiments, to isolate the mechanism from the fireretardant.

Some instances of the aerial retardant delivery system also include avariable flow control system that controls the discharge gate openpositions in order to provide the desired coverage level rating over adesired area of terrain. Some embodiments of the control system accountfor many variables in deploying the retardant. For example, the systemmay compensate for aircraft speed, altitude, pitch, and location (GPS).Furthermore, the system may compensate for retardant viscosity, volumeof retardant, pressure differential between retardant (cabin pressure)and exterior of the aircraft, and discharge gate position feedback. Thecontrol system also includes, in certain systems, safety features forprotecting the aircraft and pilot. The control system may include apressure differential interlock that prevents the discharge gates fromopening if the pressure differential between cabin pressure and exteriorpressure is too great. The control system also may also protect thefuselage by controlling the discharge of retardant in order to reducethe oil canning effect that can occur if the cabin pressure changesrapidly. If the cabin pressure changes too rapidly it can cause thewalls of the fuselage to “oil can” or move back and forth. Repeated oilcanning can fatigue the airframe and thus reduce the life of theaircraft.

In an embodiment, the aerial retardant delivery system comprises aretardant tank mountable in the fuselage of an aircraft. The retardanttank includes at least one pressure opening in fluid communication withthe fuselage such that pressure in the fuselage may act on retardantcontained in the retardant tank. The tank includes at least one outletextending through a sidewall of the aircraft's fuselage, through whichretardant may be delivered to a target. The system may also include atleast one discharge gate operative to selectively open and close theoutlet. An actuation mechanism may be disposed on the exterior of thetank and operatively coupled to the at least one discharge gate. Avariable flow controller may control the discharge gate open position inorder to provide retardant over a desired area of terrain. The systemmay further comprise a one-way flapper disposed in the pressure openingthat is operative to allow pressure in the fuselage to enter the tankwhile inhibiting retardant from spilling from the tank.

In an embodiment, the tank is configured as a polygonal funnel. In someinstances, the tank includes a main portion having a top wall and aplurality of surrounding sidewalls extending from the top wall and aneck portion extending from the main portion of the tank and extendingthrough the sidewall of the fuselage.

In an embodiment, the variable flow controller may include a pressuredifferential interlock whereby the discharge gate is not opened if thedifference in pressure between the pressure in the fuselage and ambientpressure exceeds a selected threshold level.

Also contemplated is an aircraft for delivering fire retardant to atarget area. In an embodiment the aircraft comprises a fuselage having asurrounding sidewall and at least one engine. The aircraft includes afuselage pressurization system that is operative to selectivelypressurize at least a portion of the fuselage. A retardant tank isdisposed in the fuselage that includes at least one pressure opening influid communication with the fuselage such that pressure in the fuselagemay act on retardant contained in the retardant tank. At least oneoutlet extends through the sidewall of the fuselage, through whichretardant may be delivered to the target. At least one discharge gatemay be included that is operative to selectively open and close theoutlet.

A method of delivering retardant to a target with an aircraft is alsoprovided herein. In an embodiment, the method comprises containing aquantity of retardant within a storage region of the aircraft,pressurizing an interior region of the aircraft, causing the interiorregion and the storage region to be in fluid communication, andselectively discharging the quantity of retardant from the storageregion under the influence of pressure from the interior region. In anembodiment, the retardant is allowed to discharge from the storageregion only when the difference in pressure between the pressure in theinterior region and ambient pressure is within a selected thresholdlevel.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of an aerial fireretardant delivery system and together with the description, serve toexplain the principles and operation thereof. Like items in the drawingsare generally referred to using the same numerical reference.

FIG. 1 is a partial perspective cutaway view of an aircraft equippedwith the fire retardant delivery system according to an exemplaryembodiment;

FIG. 2 is a cross section view of the aircraft fuselage taken about line2-2 in FIG. 1 showing the placement of the retardant tank;

FIG. 3 is a partial cross section view of the aircraft fuselage takenabout line 3-3 in FIG. 2;

FIG. 4 is a side view in elevation of the aircraft showing the placementof the retardant tank relative to the aircraft's frame stations andcenter of gravity datum;

FIG. 5 is a perspective view of the retardant tank according to anexemplary embodiment;

FIG. 6 is an enlarged partial perspective view of the one-way pressurevalves according to an exemplary embodiment;

FIG. 7 is a partial cross section view of the fuselage similar to thatof FIG. 2 illustrating the gate modules according to an exemplaryembodiment;

FIG. 8 is an enlarged end view of a gate module shown in FIG. 7;

FIG. 9 is a perspective view of a gate module shown in FIGS. 7 and 8;

FIG. 10 is an enlarged partial perspective view of the gate actuationmechanism according to an exemplary embodiment;

FIG. 11 is a front view of a console control panel;

FIG. 12 is an illustration of a console touch screen representing thenormal mode screen;

FIG. 13 is an illustration of a console touch screen representing thefractional mode screen;

FIG. 14 is a perspective view of a cockpit indicator module;

FIG. 15 is a top plan view of a discharge gate module according to asecond exemplary embodiment;

FIG. 16 is an end view of the discharge gate module shown in FIG. 15;

FIG. 17 is a side view in elevation of the discharge gate module shownin FIGS. 15 and 16;

FIG. 18 is a partial cut-away cross-section of the discharge gate moduletaken about line 18-18 in FIG. 15;

FIG. 19 is a perspective view of the discharge gate module shown inFIGS. 15-18;

FIG. 20 is a cross-section of the actuator mechanism taken about line20-20 in FIG. 18; and

FIG. 21 is a bottom view of discharge gate as viewed from line 21-21 ofFIG. 18.

DETAILED DESCRIPTION

Provided herein is an aerial fire retardant delivery system for safelydelivering a desired coverage level of retardant to an area of terrainthreatened by wildfire. The disclosed aerial fire retardant deliverysystem includes gate modules that are configured for improved dischargecharacteristics as well as gate mechanism reliability and ease ofmaintenance. The aerial retardant delivery system also includes avariable flow control system that controls the discharge gate openpositions in order to provide the desired coverage level rating over adesired area of terrain. The control system includes a pressuredifferential interlock and anti-oil canning technology further describedherein. While the various embodiments are described with respect to fireretardant, this should not be construed as limiting and other fluidic orparticulate substances, for example, may be deployed from an aircraftusing the apparatuses and methods disclosed herein.

FIG. 1 illustrates an aircraft 10 equipped with aerial retardantdelivery system 20 according to an exemplary embodiment. System 20comprises a storage region, in the form of retardant tank 40, with gatemodules 60. The system is controlled by variable flow control system 80located in the aircraft cockpit 2. Control system 80 may include acontroller in the form of an integrated computer module and controlscreen or separate computer, control screens, and interfaces and controlpanels. The retardant tank 40 is located in the interior 7 of thefuselage 4 at an appropriate location in accounting for the weight andbalance limits of the particular aircraft. In this case, the tank islocated near the wings 6 in order to locate the tank 40 near theaircraft's center of gravity. With further reference to FIGS. 2 and 3 itcan be appreciated that in this embodiment a majority of tank 40 islocated in the fuselage above floor decking 5. A portion of tank 40extends through decking 5 and extends beneath the underside of theaircraft. As best shown in FIG. 3, tank 40 is, in this embodiment,located forward of the wheel well area 8. FIG. 4 is a side view of theaircraft illustrating the location of tank 40 relative to the air framestations and the center of gravity 9. While the embodiments herein aredescribed with respect to a particular aircraft, in this case a BAe 146,other aircraft may be used as an aerial tanker. It should be appreciatedwith respect to FIGS. 1-4 that tank 40 is exposed via pressure openingsin the tank to cabin pressure P that, in some aircraft, is provided bythe aircraft's engines to the interior 7 of fuselage 4.

Cabin pressure P is used to assist the discharge of retardant containedin tank 40 from the aircraft. The cabin pressure P is generally greaterthan the pressure outside the aircraft's fuselage thereby creating apressure differential. FIG. 5 illustrates a plurality of one-way flappervalves 50(1)-50(6) disposed in the pressure openings. With continuedreference to FIG. 6 it can be seen that flapper valves 50 each include adoor 52 that is rotatably attached to the tank 40 with a hinge, such asa piano hinge. The flapper is installed on the inside of the tank suchthat it can only open inward against spring 56, which acts to bias door52 in the closed position. Therefore, as the tank is opened toatmospheric pressure, cabin air at cabin pressure P is allowed to enterthe tank through the pressure openings, thereby assisting in dischargingretardant from the tank. Returning briefly to FIG. 5 it can beappreciated that tank 40 is configured as a polygonal funnel. Tank 40includes a main portion having a top wall 42, through which flappervalves 50 open into the interior of the tank. Extending from top wall 42are a plurality of surrounding sidewalls 44(1)-44(4). Neck portion 46(also referred to as throat portion 46) extends from the main portion ofthe tank and extends through the floor of the aircraft and extendsthrough a sidewall of the fuselage. It can be appreciate from thefigures that tank 40 has a funnel shape configured to further assist theefficient flow of retardant from tank 40.

As shown in FIG. 7, this embodiment includes a pair of discharge gatemodules 60(1) and 60(2) disposed on neck portion 46 adjacent an outletof the tank. Gate modules 60 control the flow of retardant leaving tank40. As will be described more fully below, the gates are controlled bycontrol system 80, located generally in the cockpit of the aircraft. Thecontrol system measures a plurality of variables in order toefficiently, safely, and accurately disperse the retardant over thetarget area. FIG. 8 is an enlarged side view of discharge gate module60(1), which shows the module with one of two gates open. Accordingly,the system can control the retardant discharge rate by the number ofgates that are opened as well as by how far each gate is opened.Furthermore, as can be seen in FIGS. 7-10, the gate opening mechanismsare located outside of the discharge throat 46 resulting in a cleanthroat design.

Referring to FIG. 9, gate module 60(1) includes an elongate frame 62with a channel 64 bisecting the frame to form two discharge openings 63and 65. Each discharge opening has a respective gate 72 and 74(sometimes referred to herein as doors) hingedly disposed therealong.See for example, hinge 79 in FIG. 10, which attaches gate 72 to frame62. Each gate includes a gasket 96 disposed along a peripheral margin ofthe gate in order to help seal the tank 40 against leakage. Each gate iscomprised of a center section 73 with end caps 75 disposed thereon.Tunnel 64 accommodates one of two drive shafts used to actuate thegates. Actuators 66(1) and 66(2) rotate the drive shafts to actuate gateactuation mechanisms 70(1) and 70(2) as best shown in FIG. 10.

Drive shaft 94 is supported on both ends of the frame 62 by flangebearings 90. Drive shaft 94 extends through the flange bearing 90 andconnects to a primary actuator arm 78 which in turn connects to togglearms 77. Toggle arms 77 are connected to secondary actuator arm 76,which is mounted on spindle bracket 92. Finally, the secondary actuatorarm 76 connects to the gate 72 via adjustable tie rod 71. Tie rod 71 canbe adjusted to provide the desired closing force necessary to compressgasket 96 when the gate is in the closed position. FIG. 10 shows gate 72in the open position while gate 74 is in the closed position. When thegate is in the closed position toggle arms 77 rotate over the center ofdrive shaft 94, thereby providing an over center toggle which transfersthe opening forces generated against the gate by the retardant to themechanism 70 rather than to actuator 66. As viewed from the end shown inFIG. 10, the gates are closed by rotating the drive shafts in a counterclockwise direction and opened by rotating the shafts approximately 180degrees in the clockwise direction.

The variable flow control system 80 may be implemented with an off theshelf industrial PLC (Programmable Logic Controller), such as an OmronCJ1 series PLC, which includes discrete inputs and outputs; analoginputs and outputs; and serial communication ports. In an exemplaryembodiment, the programming language may be “Ladder Logic” type symboliccode. The control system as described herein may be implemented with,for example, a PC or microcontroller based system using variousprogramming languages as appropriate. Furthermore, the system hardwaremay comprise an integrated system or a modular system of controllers andmodules as desired.

The control system provides the ability to not only equally adjust thedoor angles of the four doors but also allows asymmetrical combinationsof door opening positions to achieve any desired flow rate.

The software is preferably modular in nature to ease certification andallow expansion of functionality. The software modules are generallyorganized by function. One functional module is a self diagnosticsection. The self diagnostic section monitors the door system fordifferences between normal operational parameters vs. real-time results.The diagnostic system may monitor several operating parameters, such asdoor slew (travel) speeds and angles; remaining tank volumes regardlessof drop mode (normal or fractional); door position feedback vs. fulltravel limit switches; and tank level indication vs. tank pressure, toname a few.

The system may include the following functional modules and sub-modules,each of which is described more fully below:

Pilot Interface

-   -   System Control        -   Mode Select—Safe/Take-off/Armed            -   Coverage Level Select            -   Fractional Quantity Select        -   Pilot indication            -   Tank Quantity in pounds, gallons, bar graph            -   Mode Selected            -   Drop Switch position—Detent 1 or Detent 2

Aircraft Input

-   -   Get and parse aircraft flight data    -   Produce “G” load offset computation    -   Produce Pitch angle offset computation    -   Produce Cabin pressure differential offset computation    -   Produce speed offset computation

Door Controller

-   -   Convert coverage level values to door angular settings. (Target        positions)    -   Convert door prox measurements to angular values    -   Compare door current position to door target position and        compute output correction signal    -   Cross check door limit travels against door position prox values

Tank Quantity

-   -   Head press computation    -   Liquid level computation    -   Head//Level correlation for quantity indication    -   Predictive computation for drop—door orifice vs. time    -   Create timeouts for selectable quantity.

Diagnostic Monitor

-   -   Door Speed    -   Door Position vs. LS crosschecks    -   Tank Volume Crosscheck        -   Sensor disagreement        -   Drop dynamics Door position and time open vs. remaining tank            quantity

Control system 80 includes a console control panel 88, shown in FIG. 11,which allows the pilot to configure the display system and adjust thedrop coverage levels. The control panel 88 includes anARMED/SAFE/TAKEOFF switch 101 that allows the pilot or co-pilot toselect which operational mode the system is in. “Safe Mode” will lockthe door locks and reactivate the Ground Proximity and Gear Warningsystems. “Take-Off” will unlock the doors and activate the GroundProximity and Gear Warning circuits. “Armed” will unlock the doors andoverride the Ground Proximity and Gear Warning circuits. A CP IN/CP OUTswitch 105 allows deactivation of the co-pilot's drop switch. AFRACT/NORMAL switch 107 selects the drop mode to be used. A FILL VALOPEN light 118 indicates that the fill valve for tank loading is opened.A TANK LEAK light 116 will illuminate if there is fluid leaking into thefuselage from the tank.

The control panel 88 also includes PRIMARY CVG LVL switch 112 thatselects the coverage level used when the drop switch is pressed to thefirst detent. SECONDARY CVG LVL switch 114 selects the coverage levelused when the drop switch is pressed to the second detent. Coveragelevel selector switches 112 and 114 are preferably rotary selectorswitches. The selector switch positions are converted into the initialsettings for the four doors and are placed into variables for eachswitch. These initial settings are obtained from a look-up table storedin memory. These will be the base values that all modifiers are appliedagainst to compute target door positions. Drop quantity is selected viaa center console mounted touch screen shown in FIGS. 12 and 13. FIG. 12shows the touch screen in NORMAL mode 84 and FIG. 13 shows the touchscreen in FRACTIONAL mode 86. The screen will allow selection inincrements of 100 gallons. The Tank Quantity is preferably displayed onthe center console touch screen in both gallons and pounds.

A cockpit indicator 82, shown in FIG. 14, is provided to communicatevarious parameters to the pilot. The indicator module includes aQuantity Bar Graph 103, an ARMED light 102, an OPEN light 104, an EMPTYlight 106, a CVG A light 108, and a CVG B light 110. The Quantity BarGraph 103 is a line of LED's below graduation marks with the numbers 0,5, 10, 15, 20, 25, 30 at the major graduation marks. These numbersrepresent 100's of gallons. The ARMED light 102 is illuminated when theswitch 101 on the center console is in the “Armed” position. The OPENlight 104 is illuminated when any door is off of its closed limitswitch. The EMPTY light 106 is illuminated when the tank is empty. TheCVG A light 108 is illuminated when the drop switch is only on the firstdetent. The CVG B light 110 is illuminated when the drop switch ispushed on to the second detent.

The aircraft input module receives input from various sensors, inputdevices, and flight data. The flaps handle not in “UP” position is usedwith the ARMED mode selection to inhibit GPWS and Gear Warning System.Flight data is decoded by an interface unit that transmits the data tothe PLC via message strings. For example, the following information maybe sent to the PLC: “G” Load, Pitch Angle, Cabin Pressure Differential,Air or Ground Speed. The control system software computes the followingdata from the other variable inputs:

Produce “G” load offset computation and place in memory

Produce Pitch angle offset computation and place in memory

Produce Cabin pressure differential offset computation and place inmemory

Produce Airspeed/Groundspeed offset computation and place in memory

The door controller module continuously calculates the target doorposition values based on selected parameters. For example the followingseven parameters may be used to derive the target door position values:

1. The “A” and “B” coverage level selector switches in the cockpit

2. Master tank quantity variable

3. flight data infeed: Pitch angle

4. flight data infeed. “G” Loading

5. flight data infeed: Pressurization Differential

6. flight data infeed: Aircraft Speed.

7. Drop switch detent 1 or 2

The door target position is controlled by a variable in memory thatrepresents the desired value (angle) of the door opening. This number isderived from the coverage level “A” or “B” variable depending on weatherthe drop switch is on detent 1 or 2 (Primary/Secondary). When the dropswitch is not pressed, a “zero” value is written into the door targetposition variable. This causes the doors to close if they are open.Output commands to the proportional hydraulic control valves, whichcontrol the door actuators, are generated whenever the target doorposition and the actual door position do not match. The actual doorposition is converted and placed into a variable in memory based on thedoor position sensors.

The control system also continuously calculates and displays thequantity of retardant in the tank. The retardant level in the tank maybe measured by a sensor in the tank, such as a float sensor. The tankfloat position reading is stored in memory. The control softwarereferences the vertical position of the float against a table ofquantities located in memory. The table correlates the tank volumetricgeometry to float position. The resulting volumetric value is placed inthe “Master Tank Qty” variable in memory.

A tank head pressure reading is mathematically computed and placed in avariable in memory. Software references the pressure reading of thesensor against a table of quantities located in memory. The tablecharacterizes the tank volumetric geometry to the pressure sensed. Theresult is placed in the “Reference Quantity” variable in memory.Parameters for fractional quantity drops are created based on sameparameters as for continuous coverage operation.

FIGS. 15-21 illustrate a discharge gate module 160 according to analternative embodiment. As shown in FIG. 15, module 160 includes twodischarge gates 172 and 174. In this case, one discharge gate module 160is used, rather than two discharge gate modules as described withrespect to FIGS. 7-10. In this embodiment, the discharge gate module 160includes a frame 162 having a divider member 164. Divider member 164extends longitudinally down the length of frame 162, bisecting the frameto form two discharge openings 163 and 165. Each discharge opening has arespective gate 172 and 174 that is hingedly disposed therealong. See,for example, hinge 179 shown in FIG. 17, which attaches gate 174 toframe 162. Each gate may include a gasket disposed along a peripheralmargin of the gate in order to help provide a seal between the gate andthe tank. A plurality of actuators 166(1)-166(4) rotate the drive shafts194(1) and 194(2) to operate gate actuation mechanisms 170 (see FIG.18). In this embodiment, a pair of actuators acts on each drive shaft194(1) and 194(2). For example, actuators 166(2) and 166(4) act on driveshaft 194(2).

With further reference to FIGS. 18 and 20, the actuation mechanism 170includes a primary actuator arm 178 that is secured to drive shaft194(2). Primary actuator arm 178 connects to toggle arms 177(1) and177(2). Toggle arms 177 are connected to secondary actuator arm 176,which is mounted on spindle 192. Finally, the secondary actuator arm 176connects to the gate 174 via crank arm 171 (also see FIG. 21). When gate174 is in the closed position, toggle arms 177 rotate over the center ofdrive shaft 194(2), thereby providing an over-center toggle whichtransfers the opening forces generated against the gate by the retardantto the mechanism 170 rather than to actuators 166(4) and 166(2). Asviewed from the end shown in FIG. 18, the gate 174 is closed by rotatingthe drive shaft 194(2) in a clockwise direction, and opened by rotatingthe shaft 194(2) approximately 180 degrees in the counter-clockwisedirection. As with the embodiment shown in FIGS. 7-10, the gate openingmodule in this case is located outside of the discharge throat 46resulting in a clean throat design. Also, discharge gate module 160 maybe controlled as described above in order to provide retardant or otherpayload over a desired area of terrain.

Also contemplated herein are methods of delivering retardant to a targetwith an aircraft. The methods thus encompass the steps inherent in theabove described structures and operation thereof. Broadly, one methodmay include containing a quantity of retardant within a storage regionof the aircraft, pressurizing an interior region of the aircraft,causing the interior region and the storage region to be in fluidcommunication, and selectively discharging the quantity of retardantfrom the storage region under the influence of pressure from theinterior region. In an embodiment, the retardant is allowed to dischargefrom the storage region only when the difference in pressure between thepressure in the interior region and ambient pressure (pressurizationdifferential) is within a selected threshold level. In one embodiment,the selected threshold level may be approximately 0.5 to 1.0 psi, forexample.

Accordingly, the fire retardant delivery system has been described withsome degree of particularity directed to the exemplary embodimentsthereof. It should be appreciated that the present invention is definedby the following claims construed in light of the prior art so thatmodifications or changes may be made to the exemplary embodiments of thepresent invention without departing from the concepts contained herein.

What is claimed is:
 1. An aerial fire retardant delivery system, thesystem comprising in combination: A. an aircraft having a fuselage with(i) a fuselage exterior about an fuselage interior and (ii) a fuselageinterior pressurization system; B. a fire retardant tank having aretardant tank exterior surrounding a retardant tank interior, the fireretardant tank mounted within the aircraft and including: a fuselage airpressure delivery passage penetrating the retardant tank exterior andthe retardant tank interior in fuselage air pressure communication with(i) the fuselage interior and (ii) the retardant tank interior; and atleast one fire retardant delivery outlet extending through a sidewall ofthe fuselage; and C. at least one fire retardant discharge gate systemin communication with the fire retardant delivery outlet, wherebyfuselage air pressure within the fuselage interior provided by thefuselage interior pressurization system can pressurize the retardanttank interior.
 2. The aerial fire retardant delivery system of claim 1further comprising a one-way valve having an air entry end and an airdispensing end, the one-way valve being disposed in the fuselage airpressure delivery passage with the air entry dispensing end in airdispensable communication with the retardant tank interior.
 3. Theaerial fire retardant delivery system of claim 1 wherein (i) the fireretardant delivery outlet has a fire retardant delivery channel and (ii)the fire retardant discharge gate system has a discharge gate drivemechanism external to the fire retardant delivery channel, whereby thedischarge gate drive mechanism would not impede flow of fire retardantthrough the fire retardant delivery channel.
 4. The aerial fireretardant delivery system of claim 2 wherein (i) the fire retardantdelivery outlet has a fire retardant delivery channel and (ii) the fireretardant discharge gate system has a discharge gate drive mechanismexternal to the fire retardant delivery channel, whereby the dischargegate drive mechanism will not impede flow of fire retardant through thefire retardant delivery channel.
 5. The aerial fire retardant deliverysystem of claim 1 wherein the fire retardant discharge gate system has:(i) a moveable retardant discharge gate; (ii) a discharge gate actuatorhaving (a) a discharge gate moving section opposite an actuator drivensection and (b) a linking section intermediate the discharge gate movingsection and the actuator driven section; and (iii) a linking sectionsupport, the discharge gate actuator being moveable between a retardantdischarge gate open position and a retardant discharge gate closedposition with the linking section in supported contact with the linkingsection support, whereby the moveable retardant discharge gate can besupported by the linking section support in the retardant discharge gateclosed position.
 6. The aerial fire retardant delivery system of claim 2wherein the fire retardant discharge gate system has: (i) a moveableretardant discharge gate; (ii) a discharge gate actuator having (a) adischarge gate moving section opposite an actuator driven section and(b) a linking section intermediate the discharge gate moving section andthe actuator driven section; and (iii) a linking section support, thedischarge gate actuator being moveable between a retardant dischargegate open position and a retardant discharge gate closed position withthe linking section in supported contact with the linking sectionsupport, whereby the moveable retardant discharge gate can be supportedby the linking section support in the retardant discharge gate closedposition.
 7. The aerial fire retardant delivery system of claim 3wherein the fire retardant discharge gate system has: (i) a moveableretardant discharge gate; (ii) the discharge gate drive mechanismincludes a discharge gate actuator having (a) a discharge gate movingsection opposite an actuator driven section, (b) a linking sectionintermediate the discharge gate moving section and the actuator drivensection, and (iii) a linking section support, the discharge gate drivemechanism being moveable between a retardant discharge gate openposition and a retardant discharge gate closed position with the linkingsection in supported contact with the linking section support, wherebythe moveable retardant discharge gate can be supported by the linkingsection support in the retardant discharge gate closed position.
 8. Theaerial fire retardant delivery system of claim 4 wherein the fireretardant discharge gate system has: (i) a moveable retardant dischargegate; (ii) the discharge gate drive mechanism includes a discharge gateactuator having (a) a discharge gate moving section opposite an actuatordriven section, (b) a linking section intermediate the discharge gatemoving section and the actuator driven section, and (iii) a linkingsection support, the discharge gate drive mechanism being moveablebetween a retardant discharge gate open position and a retardantdischarge gate closed position with the linking section in supportedcontact with the linking section support, whereby the moveable retardantdischarge gate can be supported by the linking section support in theretardant discharge gate closed position.
 9. The aerial fire retardantdelivery system of claim 1 including a variable retardant flowcontroller in controlling communication with the discharge gate system.10. The aerial fire retardant delivery system of claim 2 including avariable retardant flow controller in controlling communication with thedischarge gate system.
 11. The aerial fire retardant delivery system ofclaim 3 including a variable retardant flow controller in controllingcommunication with the discharge gate drive mechanism.
 12. The aerialfire retardant delivery system of claim 5 including a variable retardantflow controller in controlling communication with the discharge gatedrive mechanism.
 13. The aerial fire retardant delivery system of claim8 including a variable retardant flow controller in controllingcommunication with the discharge gate drive mechanism.
 14. The aerialfire retardant delivery system of claim 9 wherein the variable flowcontroller includes a pressure differential interlock.
 15. The aerialfire retardant delivery system of claim 10 wherein the variable flowcontroller includes a pressure differential interlock.
 16. The aerialfire retardant delivery system of claim 11 wherein the variable flowcontroller includes a pressure differential interlock.
 17. The aerialfire retardant delivery system of claim 12 wherein the variable flowcontroller includes a pressure differential interlock.
 18. The aerialfire retardant delivery system of claim 13 wherein the variable flowcontroller includes a pressure differential interlock.
 19. The aerialfire retardant delivery system of claim 1 also having anormal/fractional drop switch.
 20. The aerial fire retardant deliverysystem of claim 2 also having a normal/fractional drop switch.
 21. Theaerial fire retardant delivery system of claim 3 also having anormal/fractional drop switch.
 22. The aerial fire retardant deliverysystem of claim 5 also having a normal/fractional drop switch.
 23. Theaerial fire retardant delivery system of claim 8 also having anormal/fractional drop switch.
 24. The aerial fire retardant deliverysystem of claim 9 also having a normal/fractional drop switch.
 25. Theaerial fire retardant delivery system of claim 14 also having anormal/fractional drop switch.
 26. The aerial fire retardant deliverysystem of claim 1 wherein the aircraft is a fixed-wing aircraft.
 27. Theaerial fire retardant delivery system of claim 2 wherein the aircraft isa fixed-wing aircraft.
 28. The aerial fire retardant delivery system ofclaim 5 wherein the aircraft is a fixed-wing aircraft.
 29. The aerialfire retardant delivery system of claim 8 wherein the aircraft is afixed-wing aircraft.
 30. The aerial fire retardant delivery system ofclaim 9 wherein the aircraft is a fixed-wing aircraft.
 31. The aerialfire retardant delivery system of claim 14 wherein the aircraft is afixed-wing aircraft.
 32. The aerial fire retardant delivery system ofclaim 19 wherein the aircraft is a fixed-wing aircraft.
 33. The aerialfire retardant delivery system of claim 24 wherein the aircraft is afixed-wing converted passenger aircraft.